JP2011052984A - Method of measuring hardness distribution and rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measurement applicable to members different variously in shape, hardening conditions, etc. and allowing the hardness distribution of the member to be precisely measured, and to provide a high-performance rolling bearing with the hardness distribution assured of bearing components. <P>SOLUTION: Ultrasonic pulses are input into an inspected material to receive reflected waves severally reflected at respective depth positions between the surface of the inspected material and its center, thereby obtaining the intensities of the respective reflected waves. Further, the time between the inputting of an ultrasonic pulse and the receiving of a reflected wave is measured as to each of the reflected waves to calculate at which depth positions the reflected waves are reflected. By using the intensities of the respective reflected waves and the depth positions at which the waves are reflected, a reflected-wave curve is drawn showing a relation between the distance from the surface of the inspected material and the intensities of the reflected waves. Based on a correlation between the intensities of the reflected waves and the ratio of non-hardened structure and a correlation between the ratio of non-hardened structure and hardness previously obtained by using a standard material, the intensities of the reflected waves are converted into hardness to obtain a hardness distribution curve of the inspected material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for measuring and detecting the hardness distribution and heat treatment abnormality of a member without breaking. The present invention also relates to a rolling bearing in which the hardness distribution of bearing parts (inner ring, outer ring, rolling element) is guaranteed.

As a method of measuring the effective hardened layer depth in a steel member that has been subjected to induction hardening or the like, a method of observing macroscopically by etching a cut surface of a cut steel member, or each depth of the cut surface A method for measuring the hardness of the vertical position is known. However, such a destructive inspection requires a lot of time and cost because cutting is not easy when the shape of the steel member is complicated or large. Therefore, in recent years, nondestructive inspection using ultrasonic waves is sometimes used.

For example, Patent Document 1 discloses a sensor unit having a probe that transmits and receives an ultrasonic pulse having a frequency in the MHz band inclined with respect to the surface of the measurement target material, and a received signal reflected in the measurement target material. An extraction means for extracting the reflected wave from the boundary between the quench hardened layer and the base material layer (non-quenched layer) of the material to be measured, and an arithmetic unit for measuring the distance from the surface of the material to be measured to the reflected wave A layer thickness measuring apparatus using ultrasonic transverse waves is disclosed.

According to Patent Document 1, when an ultrasonic pulse propagates inside a material to be measured, a base material layer having a large crystal grain size has a higher reflection level than a quenched hardened layer having a small crystal grain size. The effective hardened layer depth can be measured by detecting a boundary where a difference is seen in the reflection level by using. Patent Document 2 discloses a method for evaluating the depth of a hardened and hardened layer using an ultrasonic wave reflected near the boundary between the hardened and hardened layer and the base material layer, as in Patent Document 1. Has been. According to Patent Document 2, a plurality of times from the surface reflected wave of the hardened hardening layer of the received signal to the ultrasonic reflected wave near the boundary received next to the surface reflected wave are measured, and the measured time information is totaled. Thus, a histogram can be formed based on the frequency of occurrence of ultrasonic reflected waves for each predetermined time zone, and the depth of the hardened hardened layer can be evaluated based on the time zone value at the peak position of the frequency of occurrence.

However, in the methods of Patent Documents 1 and 2, only one point of the cured layer depth can be measured among the materials to be measured, and the hardness is unclear. In order to ensure the necessary performance such as rolling fatigue life, the effective hardened layer depth (depth of the predetermined hardness) is measured with high accuracy in the bearing parts of the induction-hardened rolling bearing. Since it is necessary to reliably detect the presence of an incompletely quenched structure such as trustite and untransformed ferrite in the surface portion and a heat treatment abnormality such as penetration of the hardened layer (that is, a submerged state), detection patent documents 1 and 2 This method was insufficient as a method for assuring the quality of rolling bearings.

From such a background, the peak signal of the scattered wave in the reflected wave of the received ultrasonic wave is detected, and the peak position, which is the depth position from the surface where this peak signal appears, is detected from transmission to reception of the detected peak signal. Based on the correlation between the calculated ultrasonic depth position and the effective hardened layer depth. A method for measuring the hardened layer depth has been proposed (see Patent Document 3).

JP-A-8-94344 Japanese Patent Laid-Open No. 11-94809 JP 2007-198822 A

However, in the method of Patent Document 3, it is impossible to detect the above-described abnormality of heat treatment. For example, when the shape of the member or the induction hardening condition changes, and the temperature gradient during induction heating changes, the ultrasonic depth position Therefore, there is a possibility that the effective hardened layer depth cannot be accurately measured. Therefore, the present invention solves the problems of the prior art as described above, and can be applied to members having different shapes, quenching conditions, etc., and detects heat treatment abnormality and accurately measures the hardness distribution of the members. It is an object of the present invention to provide a measurement method that can be used. Another object of the present invention is to provide a high-performance rolling bearing in which the hardness distribution of bearing parts is guaranteed.

In order to solve the above problems, the present invention has the following configuration. That is, in the hardness distribution measuring method of the present invention, an ultrasonic pulse is incident on a test material, and reflected waves reflected at respective depth positions between the surface of the test material and a predetermined depth are received. Obtaining the intensity of each reflected wave, and based on the correlation between the hardness and the intensity of the reflected wave acquired in advance using a standard material that is the same material as the test material, The hardness at each depth position is obtained, and the hardness distribution in the depth direction of the test material is obtained. Further, the detection method of the heat treatment abnormality is that (the peak signal intensity of the reflected waveform caused by the non-quenched tissue (heart tissue)) / (the lowest signal intensity of the reflected waveform caused by the quenched tissue) is a predetermined value or more. When it is, it is determined that the product is a non-defective product.

In the hardness distribution measurement method and the heat treatment abnormality detection method of the present invention, the relationship between the distance from the surface of the test material and the intensity of the reflected wave is shown using the acquired intensity of each reflected wave. Draw a reflected waveform curve, by continuously entering the ultrasonic pulse a plurality of times, after obtaining a plurality of the reflected waveform curves, smoothing the averaged curve obtained by averaging the plurality of reflected waveform curves, It is preferable to use the intensity of the reflected wave read from the smoothing curve.

The kind of the test material is not particularly limited, and the hardness distribution measurement method and the heat treatment abnormality detection method of the present invention can be applied to a test material of any material, but are quenched. It is particularly suitable for steel. The kind of quenching is not particularly limited, but induction quenching is preferable. Furthermore, in the hardness distribution measurement method and the heat treatment abnormality detection method of the present invention, the test material includes a quenched structure and a non-quenched structure generated by quenching, and a ratio of the non-quenched structure in the entire structure is the above-described ratio. It is preferable that the position varies depending on the depth position, and the hardness distribution measurement method uses a correlation between the intensity of the reflected wave obtained in advance using the standard material and the ratio of the non-hardened structure and the ratio of the non-hardened structure and the hardness. It is preferable to obtain the hardness at each depth position from the intensity of each reflected wave based on the correlation.

Furthermore, the test material may be an inner ring, an outer ring, or a rolling element of a rolling bearing. Furthermore, a rolling bearing according to the present invention is a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to freely roll between the inner ring and the outer ring, and includes an inner ring, an outer ring, and a rolling element. At least one of the hardness distributions is measured by the hardness distribution measuring method.

The hardness distribution measurement method and the heat treatment abnormality detection method of the present invention can be applied to members having different shapes, quenching conditions, and the like, and the hardness distribution of the members can be accurately measured. Further, the rolling bearing of the present invention has high performance because the hardness distribution of the bearing parts is guaranteed.

It is a longitudinal cross-sectional view which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling bearing which concerns on this invention. It is the graph which showed typically the relationship between the distance from the surface, and hardness about the to-be-quenched test material. It is a graph which shows the correlation with the intensity | strength of the reflected wave in a standard material, and the ratio of a non-hardened structure | tissue. It is a graph which shows the correlation with the ratio of the non-hardened structure | tissue in a standard material, and hardness. It is the reflected waveform curve of a test material, its average curve, and a smoothing curve. It is a hardness distribution curve of a test material.

Embodiments of a hardness distribution measurement method, a heat treatment abnormality detection method, and a rolling bearing according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing the structure of a deep groove ball bearing which is an embodiment of a rolling bearing according to the present invention. The deep groove ball bearing shown in FIG. 1 is rotatable between an inner ring 1 having a raceway surface 1a on an outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a on an inner peripheral surface, and both raceway surfaces 1a and 2a. A plurality of rolling elements (balls) 3 disposed on the inner ring 1, a retainer 4 that holds the rolling elements 3 between the inner ring 1 and the outer ring 2, and a sealing device 5 that covers an opening in a gap between the inner ring 1 and the outer ring 2. 5 (for example, a steel shield or rubber seal), and in a bearing inner space formed between the outer peripheral surface of the inner ring 1 and the inner peripheral surface of the outer ring 2, a lubricant (for example, lubricating oil, Grease) is enclosed. Note that the cage 4 and the sealing device 5 may not be provided.

In this deep groove ball bearing, the inner ring 1, the outer ring 2, and the rolling element 3 are made of steel such as S53C and SUJ2. The inner ring 1, the outer ring 2, and the rolling element 3 are subjected to quenching such as carburizing quenching, carbonitriding quenching, and induction quenching, and a hardened layer (not shown) cured by the quenching has a raceway surface 1 a, 2a and the rolling surface 3a of the rolling element 3 are formed. In addition, there is a core (not shown) that is not quenched inside the hardened layer. The hardened layer has a hardened structure, and the core has a non-hardened structure.

In the prior art described above, a two-layer structure of a hardened layer and a core is assumed, and the depth position where the reflected wave due to the non-hardened structure is detected is considered to be the boundary portion of the two layers. It was. However, in reality, it does not have a complete two-layer structure of the hardened layer and the core, and there is a mixed structure layer in which hardened and non-hardened structures are mixed between the hardened layer and the core. To do. In this mixed tissue layer, the ratio of the non-hardened tissue gradually increases as the distance from the surface side toward the core side (that is, as the distance from the surface increases), and the hardness gradually increases accordingly. descend. A graph schematically showing the relationship between the distance from the surface and the hardness is shown in FIG.

In this deep groove ball bearing, the hardness distribution and heat treatment abnormality of the inner ring 1, the outer ring 2, and the rolling element 3 are measured by the following method, and the quality is guaranteed. The quality of at least one of the inner ring 1, the outer ring 2, and the rolling element 3 may be guaranteed, but it is most preferable that all the quality is guaranteed. An ultrasonic pulse of a predetermined frequency (for example, 10 MHz) is incident on the inner ring 1, the outer ring 2, and the raceway surfaces 1a, 2a and the rolling surface 3a of the rolling element 3 (hereinafter referred to as a test material), and the reflection thereof. Receive waves. The ultrasonic pulse incident on the test material is reflected at each depth position between the surface of the test material and the heart, so each reflected wave is received and the intensity of each reflected wave is acquired. To do. Further, the time from the incidence of the ultrasonic pulse to the reception of the reflected wave is measured for each reflected wave. Based on the time until reception of the reflected wave, it is possible to calculate at which depth position the reflected wave is reflected. In this way, since the intensity and the reflected depth position are obtained for each reflected wave, a reflection waveform curve showing the relationship between the distance from the surface of the test material and the intensity of the reflected wave is drawn.

And based on the correlation between the intensity of the reflected wave and the ratio of the non-quenched structure and the correlation between the ratio of the non-quenched structure and the hardness obtained in advance using a standard material to be described later, the intensity of the reflected wave is determined as hardness. Since it is possible to determine the hardness of each depth position of the test material, the reflection waveform curve can be converted into a hardness distribution curve (hardness distribution in the depth direction) of the test material. it can. FIG. 3 is a graph showing the correlation between the intensity of the reflected wave in the standard material and the ratio (area ratio) of the non-quenched structure. FIG. 4 shows the ratio (area ratio) and hardness of the non-quenched structure in the standard material. It is a graph which shows correlation of these. As can be seen from FIG. 3, the greater the ratio of the non-quenched tissue in the entire tissue, the greater the intensity of the reflected wave. In addition, the numerical value of the intensity in the graph of FIG. 3 is defined such that the lowest intensity (reflected wave caused by the quenched structure) is 0 and the highest intensity (reflected wave caused by the non-quenched structure) is 1 among the received reflected waves. The relative value is shown. Further, among the received reflected waves, the value of (the highest intensity (absolute value) caused by non-quenched tissue) / (the lowest intensity (absolute value) caused by quenched tissue) is greater than or equal to a predetermined value. It can be determined that there is no heat treatment abnormality (that is, not an incompletely quenched structure such as truthite or untransformed ferrite on the surface, or a state in which the quenched layer penetrates (ie, a fully quenched state)). For example, if the predetermined value is “2”, when the reflected waveform curve shown in FIG. 5 is obtained, it can be determined that the sample is a non-defective product.

Since even if an ultrasonic pulse is incident once, a reflected waveform curve cannot be drawn from the obtained data, an ultrasonic pulse is continuously incident a plurality of times to obtain a reflected waveform curve. One reflected waveform contains noise due to the surface condition of the subject, variations in the metal structure, non-metallic inclusions, etc., so to obtain a highly accurate hardness distribution or accurately distinguish abnormal tissues, In order to remove the noise, it is preferable to use a plurality of reflected waveform curves obtained by performing a plurality of continuous incidences a plurality of times.

That is, a plurality of reflected waveform curves are averaged to obtain one averaged curve, and a smoothed curve obtained by smoothing the averaged curve is used (see FIG. 5). That is, if the intensity of the reflected wave read from the smoothing curve is converted to hardness based on the graphs of FIGS. 3 and 4, the hardness at each depth position of the test material can be obtained. Can be converted into a hardness distribution curve of the test material. It is also possible to determine whether the product is a non-defective product based on the value of ((the highest strength attributed to the non-quenched structure (absolute value)) / (the lowest intensity attributed to the quenched structure (absolute value))). When smoothing the averaging curve, it is preferable to use a weighted average method or an exponential weighted average method, for example, by preparing a reference sample of the same material as the subject and dividing it by the reference waveform obtained from the reference sample. However, in this method, the reference sample needs to have not only the material but also the surface condition of the object, that is, the surface condition of the object varies. Therefore, it is necessary to prepare reference samples of various surface states for a certain material, and it is practically impossible to make the state of the metal structure and the state of non-metallic inclusions the same. , The method of noise reduction in the measurement accuracy may become insufficient. The present invention is a simple method regardless of the respective elements causes noise, and is a technique which can effectively remove the noise.

For example, in the smoothing curve of FIG. 5, between the depth position where the intensity of the reflected wave is 0 and the depth position where the intensity of the reflected wave is 1, the intensity of the reflected wave is 3 points (r1, r2, r3) Select. Then, from FIG. 5, the distances D1, D2, D3 from the surface corresponding to the intensity r1, r2, r3 of the reflected wave, that is, the distance from the surface at the depth position where the three reflected waves are reflected (Dt is The distance from the surface of the depth position where the reflected wave having an intensity of 1 was reflected).

Next, using the graph of FIG. 3, the strengths r1, r2, r3 and strength 1 are converted into the ratios R1, R2, R3 and the ratio 100 (%) of the non-hardened structure, and the ratio R1 of the obtained non-hardened structure , R2, R3 and the ratio 100 (%) are converted into hardness (Hv) H1, H2, H3 and core hardness using the graph of FIG. Then, the hardness distribution curve of FIG. 6 is obtained from the distances D1, D2, D3, and Dt from the surface, the hardness (Hv) H1, H2, H3, and the core hardness.

In this way, since the hardness distribution can be directly measured, it is possible to measure the hardness distribution of the test material with high accuracy in a non-destructive manner. In the above example, between the depth position where the intensity of the reflected wave is 0 and the depth position where the intensity of the reflected wave is 1, three points of the intensity of the reflected wave are selected to obtain the hardness distribution curve. Although obtained, it is not limited to three points, and if it is desired to obtain a continuous hardness distribution curve, a larger number of points may be selected. For example, when it is desired to measure only a depth position having a specific hardness such as the effective hardened layer depth, the intensity of the reflected wave corresponding to the hardness may be selected.

The apparatus for performing the incidence of the ultrasonic pulse, the reception of the reflected wave, and the acquisition of the reflected waveform curve is not particularly limited. If this apparatus is used, an ultrasonic pulse can be continuously incident from the probe onto the surface of the specimen by a local water immersion method. In this case, it is preferable that the ultrasonic pulse is continuously incident while scanning using the two-dimensional flaw detection mode (B scope mode) of the apparatus. Moreover, if this apparatus is used, the reflected wave reflected in each depth position inside the test material can be continuously received, and can be integrated and displayed to draw a reflected waveform curve.

Here, a method for obtaining the graphs of FIGS. 3 and 4 from the standard material will be described. First, the same material and the same shape as the test material (inner ring 1, outer ring 2, and rolling element 3) are quenched under the same conditions as in the case of the inner ring 1, outer ring 2, and rolling element 3. Prepare the material. Then, an ultrasonic pulse having the same frequency as that of the test material is incident on the standard material, and a reflection waveform curve is drawn in the same manner as the test material.

Next, this standard material was fractured, and the hardness of the fracture surface was measured using, for example, a micro Vickers hardness tester to obtain the hardness at each depth position. In addition, for example, the structure of the fracture surface is analyzed by a metal structure observation method by means of nital etching or electron beam backscatter diffraction (EBSP), and a non-quenched structure in all structures (hardened structure and non-hardened structure) at each depth position. The ratio was obtained. Then, from the obtained data and the reflection waveform curve of the standard material, the correlation between the intensity of the reflected wave in the standard material and the ratio of the non-quenched structure and the correlation between the ratio of the non-quenched structure and the hardness were obtained. (That is, the graphs of FIGS. 3 and 4 were created).

In addition, even if an ultrasonic pulse is incident once, a reflected waveform curve cannot be drawn from the obtained data. Therefore, in order to obtain a highly accurate hardness distribution, the standard material is the same as the test material. It is preferable to obtain a plurality of reflection waveform curves by performing a plurality of continuous incidences of ultrasonic pulses a plurality of times, and obtain a smoothing curve from the plurality of reflection waveform curves. And it is preferable to obtain the correlation between the intensity of the reflected wave and the ratio of the non-quenched structure and the correlation between the ratio of the non-quenched structure and the hardness by using this smoothing curve (that is, FIGS. 3 and 4). It is preferable to create a graph of

In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, an example has been described in which the hardness distribution of a steel member subjected to quenching is measured, but the hardness distribution measuring method of the present invention is not limited to a steel member subjected to quenching. The present invention can be applied to members made of any material. For example, the present invention can be applied to a steel member that has not been quenched, and can also be applied to a member made of a material other than steel.

Further, in the present embodiment, the deep groove ball bearing has been described as an example of the rolling bearing, but the present invention can be applied to various types of rolling bearings. For example, radial rolling bearings such as angular contact ball bearings, self-aligning ball bearings, self-aligning roller bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, and thrust types such as thrust ball bearings and thrust roller bearings This is a rolling bearing.

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Raceway surface 2 Outer ring 2a Raceway surface 3 Rolling element 3a Rolling surface

Claims (7)

An ultrasonic pulse is incident on the test material, the reflected wave reflected at each depth position between the surface of the test material and a predetermined depth is received, and the intensity of each reflected wave is acquired, Based on the correlation between the hardness acquired in advance using the same standard material as the test material and the intensity of the reflected wave, the hardness of each depth position is determined from the intensity of each reflected wave, A hardness distribution measuring method characterized by obtaining a hardness distribution in the depth direction of a specimen. Using the acquired intensity of each reflected wave, a reflected waveform curve showing the relationship between the distance from the surface of the test material and the intensity of the reflected wave is drawn, and the ultrasonic pulse is continuously incident a plurality of times. Thus, after obtaining a plurality of the reflected waveform curves, smoothing the averaged curve obtained by averaging the plurality of reflected waveform curves, using the intensity of the reflected wave read from the smoothed curve, 2. The hardness distribution measuring method according to claim 1, wherein the hardness at the depth position is obtained. The hardness distribution measuring method according to claim 1, wherein the test material is a hardened steel material. The hardness distribution measuring method according to claim 3, wherein the quenching is induction quenching. The test material includes a quenched structure and a non-quenched structure generated by quenching, and the ratio of the non-quenched structure in the entire structure varies depending on the depth position, and the reflected wave obtained in advance using the standard material. The hardness at each depth position is obtained from the intensity of each reflected wave based on the correlation between the strength and the ratio of the non-quenched structure and the correlation between the ratio of the non-quenched structure and the hardness. The hardness distribution measuring method according to claim 3 or claim 4. The hardness distribution measuring method according to any one of claims 1 to 5, wherein the test material is an inner ring, an outer ring, or a rolling element of a rolling bearing. In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged so as to be able to roll between the inner ring and the outer ring, at least one of the inner ring, the outer ring, and the rolling element is defined in claims 1 to 5. A rolling bearing, wherein the hardness distribution is measured by the hardness distribution measuring method according to any one of the above.

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